Processes for the preparation of propylene from a hydrocarbon feed are well known in the art.
The processing of hydrocarbon feeds containing C5 and/or C6 cycloalkanes, however, is found to be difficult. For example, in their presentation on PROPYLUR technology H. Boelt et al. indicated that paraffins, cycloalkanes, cycloalkenes and aromatics can be contained in the feedstock and pass a reactor with nearly no conversion. (see H. Boelt et al. “Recent developments in propylene technologies, part II: PROPYLUR technology, Linde European Olefin Seminar, Penha Longha (Portugal), November 2001).
In EP-A-0788838 the catalytic conversion of a raw material naphtha feed is described. In the examples raw material naphtha was converted with several ZSM-5 type zeolites, having silica to alumina ratio's ranging from about 30 to about 126. In order to obtain high yields of ethylene and propylene the use of a group Ib metal promotor such as silver was found essential. Although, in passing other zeolites such as ZSM-23 and ZSM-35 were mentioned, the use of such zeolites was not actually disclosed. The only zeolite used in the examples was ZSM-5.
In U.S. Pat. No. 6,307,117 the necessity of a group Ib metal promotor such as silver for a high yield conversion of a hydrocarbon feed to ethylene and propylene was confirmed. It was furthermore found necessary that the zeolites had a silica to alumina ratio in the range from 200 to 5000. Although, in passing other zeolites such as ZSM-23 and ZSM-35 were mentioned, the use of such zeolites was not actually disclosed. The only zeolite used in the examples was ZSM-5.
In example 10 of U.S. Pat. No. 6,307,117 a cyclopentane feed was cracked into smaller components over a ZSM-5 catalyst having a silica to alumina ratio of 300. The product included propylene and butylene in a weight ratio of propylene to butylene of about 1.6.
U.S. Pat. No. 6,339,181, describes a process for the preparation of propylene from a hydrocarbon feed stream containing C5 and C6 components. It is mentioned that cycloparaffins can be present in the feed, however, the patent only discloses conversion of olefins. Furthermore, although in passing other zeolites such as ZSM-23 and ZSM-35 were mentioned, the use of such zeolites was not actually disclosed. The only zeolite used in the examples was ZSM-5. The examples only disclose conversion of feed streams containing paraffins and olefins but no cycloparaffins. In the non-comparative examples the C5/C6 cut was only contacted with a SAPO-11 catalyst. The product included propylene and butylene in a propylene to butylene weight ratio in the range from about 1.4 to about 3.8.
US-A-2002/0063082 describes a method for converting a naphtha feed having naphthene ring-containing compounds (s.i.c) by first contacting the naphtha feed with a ring opening catalyst, comprising e.g. Ru, Rh, Ir, or Pt to form a ring-opened product, whereafter this ring opened product can be catalytically cracked by a medium pore crystalline silicate zeolite catalyst. It would be useful to have a process wherein such a naphtha feed can be directly converted into propylene.
It would be desirable to have a process that would be able to convert a hydrocarbon feedstock containing C5 and/or C6 cycloalkanes in an economically viable manner in high selectivity into propylene with little co-production of undesirable butene-byproducts.